Staff member
Jun 3, 2020
A vug (also called as vugh or vugg) is a cavity, void or a large pore in a rock that is usually lined with mineral precipitates. The vugs can be formed due to a variety of processes such as through faulting, folding, or collapse of a rock– and are often partially filled with secondary minerals. The cracks and fissures developed due to tectonic activity, open spaces within breccias, and removal of minerals due to erosion or dissolution are the common examples of vugs. The crystal development depends on the open space and slow cooling of mineral solution.

vug geology

The rocks contain various types of openings on their surface ranging from minor fractures to a large holes. All these openings are not called as vugs as there are other terms used for some of them such as ruse, geode, mold, pit, pocket, pore, vesicle, and phoload. The vugs can be identified as the openings in rocks usually filled with secondary minerals. The formation of these minerals happens at a later stage after the formation of the rock. The vugs appear like cavities formed due to removal of minerals or crystals in the rocks.

The vugs are formed when openings are developed in the rocks due to tectonic processes, erosion, or dissolution. The minerals or crystals are removed from the rocks resulting in the formation of cavities. Most vugs are filled with mineral solution which flows through the rock due to natural processes. The mineralization happens in later stages when the crystals are formed in the vugs. The common minerals like quartz and calcite usually form within the voids.

Difference between vugs and other openings
The rocks contain several openings and many of them resemble vugs due to a similar appearance. Vugs are cavities in rocks filled with different types of minerals. Vesicles are cavities formed in volcanic igneous rocks due to the escaping gases, resulting in a sponge like appearance. Geodes are small cavities commonly found in limestone with a druzy lining of calcite or quartz crystals. The term "geode" is usually reserved for round crystal-lined cavities in sedimentary rocks and ancient lava. Druses are small cavities lined with crystals of same mineral found in the host rock. Miarolitic cavities are openings on coarse-grained igneous rocks that are lined with crystals of the same minerals of the host rock.

James Smith

Jun 22, 2020
Vug vs Geode is a common argument as they both are similar. Vugs are cavities in rocks filled with secondary minerals, where as Geodes are cavities in rocks filled with well-developed crystals.


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